The present invention pertains to an arrangement and method for correcting errors in teletext signals.
More specifically, the present invention relates to a method of correcting errors in the individual bytes of teletext signals which are received successively and periodically page by page. After the teletext signals are decoded, they are stored page by page into first segments of a page memory of a television receiver. Each segment is designed to hold one page. A teletext page to be displayed on the television screen is selected from the page memory in response to a page selection signal. Erroneous characters are detected by parity checks of the bytes and indicated as blank characters which are replaced by correct characters contained in the same page at the next instant reception.
Such a correcting method is described in the journal "Funkschau", 1977, pages 820 to 824 and 882 to 887, especially page 885, right column at the top. As shown in FIG. 18 on page 885, it can be seen that the bytes are fed to the page memory without the parity bit but are fed to the parity checker with the parity bit. The output signal of the parity checker is applied through an AND gate to the write enable input of the page memory, i.e., only if a correct parity is detected will the bytes be stored into the page memory. In case of incorrect parity, the respective location will remain disabled, so that a blank character will appear on the television screen.
By means of the parity check, only a single error in each byte can be detected, while double errors go unnoticed.